Boris Johnson's closest aide is poised to quit City Hall just as the Conservative mayor looks to be on the brink of securing a second term.

Guto Harri, a former BBC correspondent who became Johnson's communications director when he first won office in 2008, has confided to colleagues that he intends to leave on 14 May, according to a source close to City Hall.

Harri insisted he had "not agreed any option" amid rumours that he has been approached by News International to become director of communications.

The departure of Harri, an effective operator seen as Johnson's most trusted aide, would be a huge blow to the high-profile Conservative politician.

Harri confirmed on Friday that he had received approaches about jobs, but declined to discuss the details. He insisted he had not accepted any offers and maintained that he could still be persuaded to stay at city hall.

He said he intended to discuss his future with Johnson over the weekend if, as a succession of polls suggest, the Conservative candidate defeats his Labour rival, Ken Livingstone, for a second time after the election result is announced on Friday night.

As the electronic count in London was under way, voting returns in so far appeared to confirm recent opinion polling indicating Johnson was on course for victory.

Harri's potential departure not only raises question marks about who will fill the role if he leaves, but also speculation about offers on the table for Harri, who was approached by David Cameron five years ago to fill the director of communications role before he decided to give the job to Andy Coulson, the former editor of News of the World.

Harri left the BBC in late 2007 to work for the London public relations agency Fleishman-Hillard as a senior policy adviser, which saw him spend a week advising the Zimbabwean opposition leader, Morgan Tsvangirai. Just months later, over a chat in Johnson's back garden the week before he was elected in 2008, the mayor snapped up Harri to be his director of communications in what would prove to be one of his first appointments.

The pair met as students at the Oxford Union. Johnson was two academic years above Harri, who joined Queen's College to read Politics, Philosophy and Economics. They played rugby on opposing sides, with Johnson representing Balliol College.

The pair would go on to meet many times both as journalists and while Johnson was an MP and Harri covered the political beat.

The decision to bring Harri into City Hall proved fruitful, with the pair appearing to enjoy a close working relationship.

Johnson no doubt had Harri in the front of his mind when he later warned Cameron in the runup to the general election that he would mount a "Stalingrad-like resistance" to any move to "kidnap" members of his team.

Harri had been approached by Cameron when he was in opposition about the post of director of communications. The Tory party leader invited Harri and his family to his Oxfordshire home to discuss the role in 2007.

But despite being close to agreeing to give the post to Harri, he eventually appointed Coulson. The former News of the World editor quit early last year amid pressure about phone hacking under his watch at the paper. He was replaced by Craig Oliver, controller of BBC Global News since June 2010.

Harri, a native Welsh speaker, was born in Cardiff and received a comprehensive school education before going to Oxford. He was BBC Wales's political correspondent before moving to London to cover UK and world news for the Welsh language news service provided to S4C by the BBC.

He joined BBC News 24 as chief political correspondent in November 2002. He was based in Rome from July 2004 to January 2005 and spent two years as North America business correspondent, returning to England in the summer of 2007.